be subdivided into three sets: (1) those of the Tibiofibular articulation; (2) the interosseous membrane; (3) those of the Tibiofibular syndesmosis.

Tibiofibular Articulation (articulatio tibiofibularis; superior tibiofibular articulation).This articulation is an arthrodial joint between the lateral condyle of the tibia and the head of the fibula. The contiguous surfaces of the bones present flat, oval facets covered with cartilage and connected together by an articular capsule and by anterior and posterior ligaments.

The Articular Capsule (capsula articularis; capsular ligament).The articular capsule surrounds the articulation, being attached around the margins of the articular facets on the tibia and fibula; it is much thicker in front than behind.

The Anterior Ligament (anterior superior ligament).The anterior ligament of the head of the fibula (Fig. 347) consists of two or three broad and flat bands, which pass obliquely upward from the front of the head of the fibula to the front of the lateral condyle of the tibia.

The Posterior Ligament (posterior superior ligament).The posterior ligament of the head of the fibula (Fig. 348) is a single thick and broad band, which passes obliquely upward from the back of the head of the fibula to the back of the lateral condyle of the tibia. It is covered by the tendon of the Popliteus.

Synovial Membrane.A synovial membrane lines the capsule; it is continuous with that of the knee-joint in occasional cases when the two joints communicate.

Interosseous Membrane (membrana interossea cruris; middle tibiofibular ligament).An interosseous membrane extends between the interosseous crests of the tibia and fibula, and separates the muscles on the front from those on the back of the leg. It consists of a thin, aponeurotic lamina composed of oblique fibers, which for the most part run downward and lateralward; some few fibers, however, pass in the opposite direction. It is broader above than below. Its upper margin does not quite reach the tibiofibular joint, but presents a free concave border, above which is a large, oval aperture for the passage of the anterior tibial vessels to the front of the leg. In its lower part is an opening for the passage of the anterior peroneal vessels. It is continuous below with the interosseous ligament of the tibiofibular syndesmosis, and presents numerous perforations for the passage of small vessels. It is in relation, in front, with the Tibialis anterior, Extensor digitorum longus, Extensor hallucis proprius, Peronæus tertius, and the anterior tibial vessels and deep peroneal nerve; behind, with the Tibialis posterior and Flexor hallucis longus.

Tibiofibular Syndesmosis (syndesmosis tibiofibularis; inferior tibiofibular articulation).This syndesmosis is formed by the rough, convex surface of the medial side of the lower end of the fibula, and a rough concave surface on the lateral side of the tibia. Below, to the extent of about 4 mm. these surfaces are smooth, and covered with cartilage, which is continuous with that of the ankle-joint. The ligaments are: anterior, posterior, inferior transverse, and interosseous.

The Anterior Ligament (ligamentum malleoli lateralis anterius; anterior inferior ligament).The anterior ligament of the lateral malleolus (Fig. 355) is a flat, triangular band of fibers, broader below than above, which extends obliquely downward and lateralward between the adjacent margins of the tibia and fibula, on the front aspect of the syndesmosis. It is in relation, in front, with the Peronæus tertius, the aponeurosis of the leg, and the integument; behind, with the interosseous ligament; and lies in contact with the cartilage covering the talus.

The Posterior Ligament (ligamentum malleoli lateralis posterius; posterior inferior ligament).The posterior ligament of the lateral malleolus (Fig. 355), smaller than the preceding, is disposed in a similar manner on the posterior surface of the syndesmosis.